Belgian Pat. No. 827926 discloses inter alia clavulanic acid and its salts and esters which substance clavulanic acid has the formula (I): ##STR2##
Clavulanic acid and its salts and esters are able to inhibit .beta.-lactamases from a range of bacteria and owing to this useful property are able to enhance the effectiveness of penicillins and cephalosporins against many gram-positive and gram-negative bacteria.